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69 lines
2.2 KiB
C
69 lines
2.2 KiB
C
/************************************************************************
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**
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** @file lambdaconstants.h
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** @author Roman Telezhynskyi <dismine(at)gmail.com>
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** @date 29 1, 2022
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**
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** @brief
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** @copyright
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** This source code is part of the Valentina project, a pattern making
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** program, whose allow create and modeling patterns of clothing.
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** Copyright (C) 2022 Valentina project
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** <https://gitlab.com/smart-pattern/valentina> All Rights Reserved.
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**
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** Valentina is free software: you can redistribute it and/or modify
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** it under the terms of the GNU General Public License as published by
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** the Free Software Foundation, either version 3 of the License, or
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** (at your option) any later version.
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**
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** Valentina is distributed in the hope that it will be useful,
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** but WITHOUT ANY WARRANTY; without even the implied warranty of
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** MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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** GNU General Public License for more details.
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**
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** You should have received a copy of the GNU General Public License
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** along with Valentina. If not, see <http://www.gnu.org/licenses/>.
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**
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*************************************************************************/
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#ifndef LAMBDACONSTANTS_H
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#define LAMBDACONSTANTS_H
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/*
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given a lambda that wants to capture two constants
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const auto k1 = 1000;
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const auto k2 = 2000;
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int v = 0;
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auto lambda = [&v, &k1, &k2]() {
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v = k1 * k2;
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}
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Then unfortunately clang will correctly warn about unnecessary captures. And MSVC will fail to compile if you don't
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capture.
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https://stackoverflow.com/questions/52416362/unused-lambda-capture-warning-when-capture-is-actually-used
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An imperfect solution is to declare the lambda using the V_LAMBDA_CONSTANTS macro.
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auto lambda = [&v
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V_LAMBDA_CONSTANTS(&k1, &k2)
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](){
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v = k1 * k2;
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}
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This should work correctly. Most of the time.
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NOTE: There is no comma after the final capture variable before the V_LAMBDA_CONSTANTS macro. The macro is variadic and
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will work with 1 or more captures.
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*/
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#ifndef V_LAMBDA_CONSTANTS
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#if defined(Q_CC_MSVC)
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#define V_LAMBDA_CONSTANTS(...) ,__VA_ARGS__
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#else
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#define V_LAMBDA_CONSTANTS(...)
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#endif
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#endif
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#endif // LAMBDACONSTANTS_H
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